1. Field of the Invention
The present invention relates to an electronic endoscope apparatus capable of observing a laser-illuminated biological body portion without any halation phenomenon.
2. Description of the Related Art
Various types of electronic endoscope apparatus employing an electronic scope through which a biological body portion is illuminated, and an image sensor to produce an endoscopic image of the illuminated body portion, have been developed and are commercially available in the medical electronic field.
The aims of such electronic endoscope apparatuses are to observe an organ within a body cavity of the biological body, and also to cure the biological body in accordance with the endoscope laser curing methods, e.g., the lasing, and dissection.
As is known, in the curing observation by the laser illumination, the brightness of the laser reflected from the laser-illuminated portion of the biological body is extremely higher than that reflected from another portion around this laser-illuminated biological body portion. As a result, if the laser light reflected from the laser-illuminated biological body portion is directly received by the image sensor and the endoscopic image thereof is displayed by processing the image signal derived from this image sensor, there is induced a halation phenomenon in the endoscopic image of the laser-illuminated biological body portion, in a specific case, over the entire endoscopic image of the observed biological body.
To solve this halation difficulty, one conventional solution has been proposed, for instance, in Japanese KOKAI (Disclosure) patent application No. 62-129047 opened on June 11, 1987 and Japanese KOKAI utility model application No. 62-14231 opened on Sept. 8, 1987. That is, the laser cut filter, e.g., an infrared cut filter is positioned in the optical system employed within the distal end unit of the electronic scope so as to prevent the laser light component to be incident upon the image sensor.
Although such a halation problem can be solved by employing the laser cut filter in these conventional electronic endoscope apparatuses, another problem may newly occur. In other words, when the optical image formed by cutting out the laser light component is incident upon this image sensor to whereby display an endoscopic image of the biological body, in which the conditions of the laser-illuminated biological body portion cannot be observed from the endoscopic image thereof displayed on the monitor screen, because the optical image of the laser-illuminated biological body portion is optically lost by the laser cut filter.